The invention relates generally to paper manufacturing or the like. More particularly, the invention relates to an improved method and device for tail threading.
When starting a paper machine after a stoppage or a web break, the paper has to be passed through the machine again. Thus, a narrow edge strip is first separated from the edge of the paper web and run through the machine. After the edge strip has been made to travel through the machine or a machine section, it can be spread to a full-width web. There are various guide systems available to make the edge strip follow the travel path formed by cylinders and rolls. Generally, in that case, rope systems, so-called threading ropes, are used, which travel outside the edge of the paper web, the lead-in strip or tail being guided in between the ropes.
For example the Finnish patents 72549 and 89288 illustrate how the tail is guided after its cutting point into a gap formed by two threading ropes to pass the tail through a particular section in the longitudinal direction of the machine.
For example the process of passing the tail through multi-roll calenders sets high requirements for the threading system at high threading speeds. It can be estimated that rope threadings are suitable at speeds up to ca. 1500 m/min. At higher speeds, the narrow tail cannot be held between two adjacent ropes or cords without problems. For example, the tail is easily detached or broken when it hits parts located along its path, e.g. the shields of the threading ropes.
The purpose of the invention is to eliminate the above-presented drawbacks and to present a method which can be used in any section of a paper machine or an after-treatment machine for paper for reliable tail threading even at high threading speeds. The purpose of the invention is further to present a method which is advantageous especially in on-machine threadings of fast-running paper machines. To attain this purpose, the method for tail threading, according to the present invention, two belts are utilized which are guided against each other in such a way that the tail remains in between their surfaces. The neutral aces of the belts are substantially on the same level in the belt pair, wherein even in threadings along a tortuous path it is possible to avoid chafing of the tail. Furthermore, it is possible to utilize the shaping of the surfaces of the belts for locking the tail.
The device for attaining the objective of the invention is, in turn, characterized in what will be presented in the characterizing part of the appended claim 5. Both elongated means of the threading device are belts, wherein their surfaces which are placed against each other can be utilized to support the tail, and the neutral axes of the belts placed against each other are substantially on the same level. The belts may also be provided with formed portions, such as portions located at fixed intervals in the longitudinal direction, by means of which portions it is possible to lock the tail in a reliable manner to travel along with the belt.